The Sahel, the semi-arid region of Africa just south of the Sahara desert, has experienced such a
prolonged and devastating drought in recent decades as to be often cited in the non-scientific
literature as an example of the perils of global warming. This talk will take a closer look at the
connection between multi-decadal changes in Sahel rainfall and global climate change: I will present
an overview of the causes of the 20th century drought, and will look at projections for future
changes in Sahel rainfall in response to increasing greenhouse gases.

I will show that the 20th century long-term drying can be attributed to a combination of natural
variability and the response to anthropogenic changes in sea surface temperature (especially those
associated with changes in reflective aerosols loadings). Changes in the 21st century are dominated
by the effect of increasing greenhouse gases and are characterized by a delay and a shortening of
the rainy season---a seasonal pattern of anomalies substantially different from that of the recent
drought.

Finally, I will interpret Sahel rainfall projections in the context of a delay of the seasonal cycle
of global precipitation and SST and propose possible sources of this global phase shift.